The cryosorption vacuum pump has been known since used as a rough pump by Sir James Dewar and Thomas Edison, circa 1875. This form of usage continues to the present day; e.g., Grant et al., Review of Scientific Instruments, May 1963, pp. 587,588. In recent years there has been a great deal of interest in the usage of cryosorption pumps for the high vacuum range.
Cryosorption pumps, like cryogenic pumps, afford the advantage over ion and diffusion pumps of freedom from electrostatic and magnetic fields and freedom from pump generated hydrocarbons such as methane or pump oil. Cryosorption pumps afford the advantage over cryogenic pumps of trapping high vapor pressure gases such as nitrogen at 77.degree. K. and under high vacuum, hydrogen at 20.degree. K., etc., that would escape a cryogenic pump. Cryosorption pumping elements can be used in separate pump bodies or gas pumping elements in say, an environmental test chamber which may be thought of as a "pump" for purposes of this application.
However, the use of cryosorption in high vacuum pumping requires an effective sorbent mounting arrangement. A cryosorption pumping element must withstand cycling over a substantial temperature range, operating as a pump at 77 or 20 or even 4.2.degree. K. and then baking out at up to 200.degree. C. between pumping cycles to regenerate the sorbent. Proper selection of bond material is necessary to withstand the stress induced by these wide swings of temperature. Good bonding is also necessary to provide effective heat transfer within the pumping element. Other desired properties of cryosorption pumping elements are freedom from organic components such as conventional epoxy binders, ruggedness, economy of manufacture and exposure of substantially all the contained sorbent to the gas to be pumped.
U.S. Pat. No. 3,387,767 to Hecht, assigned in common with the subject patent, discloses the use of a sintered mass of metallic fibers which provide porous holding structure with tunnels leading to absorbent powders within.
Two major disadvantages exist for the granular sorbents, in the prior art, which are bonded to panels. First, the sorbent particles have irregular shapes which prevent uniform, secure bonding. Second, the amount of sorbent which can be bonded with good thermal contact per panel area is limited to one particle layer, which significantly restricts the ultimate volume of gas adsorbed per unit panel area.